U.S. Pat. Nos. 4,351,077 to Hofmann and 4,642,833 to Stoltz, et al., incorporated herein in their entireties by this reference, disclose automatic, water-interruption-type suction swimming pool cleaners having flexible annular discs. These discs are typically mounted near the inlets of the suction cleaners and designed to contact pool surfaces when in use. By doing so, the discs decrease the tendency of the cleaners to disengage from pool surfaces, particularly when the cleaners are negotiating transition regions between walls and floors.
U.S. Pat. No. 4,193,156 to Chauvier, also incorporated herein in its entirety by this reference, describes (at column 4, lines 5-55) an annular disc having numerous "concertina-like," "circumferentially spaced folds." These folds extend when their associated swimming pool cleaner encounters a transition region, purportedly "keeping the inflow of water into the mouth opening to a minimum." The underside of the disc is grooved, moreover, according to the Chauvier patent, to assist in removing dust from the floors and walls of swimming pools.
Other existing swimming pool cleaner discs, including one provided by Jandy Industries, Inc., contain upwardly-extending protrusions about their peripheries. The protrusions of the Jandy disc are truncated so that they do not extend beyond the disc's periphery, however, and the periphery itself is wholly circular. Another disc distributed outside the United States combines the upwardly-extending protrusions with a scalloped periphery. Again, however, the protrusions are truncated and thereby do not extend beyond the periphery of the disc. The vertical peripheral faces of the truncated protrusions of this disc function as stops, causing the disc to move around certain obstacles extending from internal pool surfaces rather than, for example, lodging under them or moving over them.